The present invention relates to liquid pumps; more particularly, the invention relates to liquid pumps adapted for pumping liquids having extremely high solids content.
Liquid pumps have long been used for pumping liquids of varying viscosities, including very low viscosity oils and paints, and medium to high viscosity liquids which have a rather slow flow characteristic. In a case of paints and other coating materials it is typical for liquid pumps to handle such materials having a solids content in the range of 30%-40%. However, when the solids content of such materials exceeds about 40% the pumping problem becomes more difficult, and special handling problems have to be taken into account. Liquid materials having higher solids content tend to build up and accumulate within the pump and can seriously degrade pumping efficiency, even to the point of disabling the pump from effective operation. It is necessary to frequently disassemble the pump components for cleaning, so as to remove accumulated solids from adhering to the various components on the interior of the pump and to return the pump to normal operating efficiency. Such pumps therefore require frequent maintenance intervals, wherein the pump must be removed from operation and disassembled for cleaning.
A particular problem in the pumping of high solids content materials has been the tendency of the solid particulates in the pumped material to build up or "pack" along portions of the interior walls of the pumping cylinder. One area where this problem has been noticed is in the region immediately adjacent the intake valve of the pump, which frequently has a void or recess which tends to be outside of the flow path of the liquid flowing through the pump. Solid particulate matter which becomes lodged in this region is not influenced by the material flow through the pump, and therefore it tends to accumulate along the interior pump walls and to gradually pack the walls with increasing amounts of material. As this buildup increases it can degrade the operating efficiency of the pump, and in extreme cases can even disable the pump from further operation.
It would be a significant advantage in the art to provide a liquid pump for pumping high solids content materials wherein the solids content may range from 70%-80%, and wherein the frequency of maintenance intervals may be reduced in order to permit the pump to continue in operation for longer time periods.
Modern coating materials having high solids content typically include particulate matter in order to provide a textured coating on a surface, and the solids content of such coating materials can include particulate matter up to and including particles such as sand or grit having a cross-sectional dimension of 2-3 millimeters (mm). Materials of this general type are exceedingly difficult to pump, not only because of the buildup of solids within the pump itself, but also because of the difficulty in maintaining a relatively steady flow of the particulate matter through the pump.